The present invention relates to the preparation of a foamed material, particularly a sulfur foam.
U.S. Pat. No. 3,337,355, issued to Dale and Ludwig, discloses the production of a sulfur foam using the following steps:
A. HEATING SULFUR TO ABOVE ITS MELTING POINT;
B. BLENDING A STABILIZING AGENT WITH THE MOLTEN SULFUR;
C. BLENDING A VISCOSITY INCREASER WITH THE MOLTEN SULFUR, STEPS (B) AND (C) BEING TAKEN IN EITHER ORDER WITH RESPECT TO THE OTHER;
D. FORMING BUBBLES IN THE MOLTEN SULFUR, AND
E. COOLING THE MOLTEN SULFUR TO BELOW ITS MELTING POINT.
Stabilizing agents disclosed include talcs, mica and plate-like particles. Viscosity increasers disclosed include phosphorus sulfide, styrene monomers and polysulfide liquids. According to U.S. Pat. No. 3,337,355:
"The forming of bubbles in the molten sulphur may be done in any conventional manner for forming foams generally such as those methods used in forming plastic foams. These include (1) mechanically mixing a gas such as air with the molten sulphur, (2) adding a blowing agent, and (3) mixing a liquid with the molten sulphur while maintaining a predetermined pressure on the sulphur and then releasing the pressure on the sulphur sufficiently that the liquid will vaporize at the temperature and lower pressure involved. All of these methods must use material free from substances having a deleterious effect upon the process. For example, most members of the halogen family will decrease the viscosity of the sulphur sufficiently that proper foams will not be formed. Examples of blowing agents that are satisfactory are a combination of sodium carbonate or bicarbonate and acid, N,N'-dimethyl N,N'-dinitrosoterephthalamide sold under the trade name Nitrosan, sodium bicarbonate dispersed in a neutral oil sold under the trade name Unicel S, and N,N'-dinitrosopentamethylenetetramine sold under the trade name Unicel ND. Nitrosan, Unicel S, and Unicel ND are products of E. I. du Pont de Nemours & Co."
According to the examples in U.S. Pat. No. 3,337,355, typical ingredients for the sulfur foam include sulfur, talc, P.sub.2 S.sub.5, calcium carbonate and phosphoric acid.
By retrospect in view of the present invention, art in the area of polyurethane foams can also be referred to by way of background. As indicated in Kirk-Othmer Encyclopedia of Chemical Technology (1965), Vol. 9, p. 853, the chemical ingredients of a urethane foam are a polyfunctional isocyanate (1) and a hydroxyl-containing polymer (2) along with catalysts to control the rate and type of reaction and other additives to control the surface chemistry of the process. A number of competing reactions can occur when (1) and (2) are brought together, but the main product, shown in the equation below, is a polyurethane (3). ##STR1##
Originally, carbon dioxide was generated in situ (by the reaction of isocyanate with water) as a blowing agent for both rigid and flexible polyurethane foams. U.S. Pat. No. 2,814,600 discloses production of polyurethane foams by reaction of isocyanate groups with water to release carbon dioxide.
It is said to still be the common practice today to rely largely on reaction of water with isocyanate as a method for gas generation for flexible materials. Rigid cellular polyurethanes are now typically produced using volatile liquids, usually fluorocarbons, which act as expanding agents, producing gas as the foaming mixture is heated by the exotherm of the reaction.
Although it is not the typical method used to make polyurethane foams, it has been disclosed to react carboxylic acid groups with isocyanate groups to form amide bonds and release carbon dioxide. See, for example, Saunders and Frisch, "Polyurethanes", Part I, Interscience Publishers (1962) at p. 79.
U.S. Pat. No. 3,222,301 discloses polyurethane foams containing a small amount of dissolved sulfur to prevent discoloration of the polyurethane foam. As can be seen from the examples of U.S. Pat. No. 3,222,301, only a very small amount of sulfur is included in the final foam; one of the reactants for formation of the foam can pick up the necessary small amount of sulfur by filtering the reactant through finely divided sulfur prior to using the reactant to form the foam.
U.S. Pat. No. 3,542,701 discloses the use of sulfur in various foams, including polystyrene foams as well as polyurethane foams, to decrease the inflammability of the foam. According to U.S. Pat. No. 3,542,701, "The total amount of elementary sulfur in the foam or other cellular structure may be as high as slightly under 50% by weight". The process of U.S. Pat. No. 3,542,701 is stated to be: " . . . applicable to all foams or other cellular or porous structures of combustible synthetic macromolecular substances, without exceptions, although the best results are obtained with substances, which at the temperatures applied in the preparation of the foams or other cellular or porous structures of these substances hardly react with sulfur if at all."
U.S. Pat. No. 2,814,600 and 3,169,119 disclose the production of polyurethane foams from arylene diisocyanates and liquid polysulfide polymers. U.S. Pat. No. 3,169,119 discloses the use of a "foam stabilizer" or surfactant, such as a silicone oil, for example a polydimethyl siloxane or an alkyl silane polyoxyalkylene block copolymer. The latter type of silicone oil is disclosed in U.S. Pat. No. 2,834,748.
U.S. Pat. No. 3,645,924 also discloses, at Col. 7, line 52 to Col. 8, line 22, surfactants which can be employed to obtain uniform cell structure in making polyurethane foams.
Similarly, U.S. Pat. No. 3,706,680 discloses the use of poly organo silicone compounds as well as polypropylene glycols as suitable surface active agents or emulsifiers that can be used in polyurethane foam production.
"Polyurethane Techology," edited by P. F. Brunes, Interscience Publishers, 1969, describes in general at pp. 50-52 the use of poly organo silicone surfactants in polyurethane foam preparation. At page 51, the following is stated: "The surfactant may be added with any of the two to six streams usually fed to the mixing head in the one-shot process. The addition of the silicone as a separate stream affords the maximum in control over loss of foam stability, since surfactant concentration may be adjusted independently of reactants and catalysts."